Airborne proximity infrared firing error indicator



AIRBORNE PROXIMITY INFRARED FIRING ERROR INDICATOR Filed Jan. 30, 1959 3 Sheets-Sheet 1 5 Sheets-Sheet 2 D. J. EDWARDS H Iv?! l|| n /////m. h- 7 Jan. 29, 1963 AIRBORNE PROXIMITY INFRARED FIRING ERROR INDICATOR Filed Jan. 30, 1959 Jan. 29, 1963 D. J. EDWARDS 3,075,726

AIRBORNE PROXIMITY'INFRARED FIRING ERROR INDICATOR Filed Jan. 30, 1959 5 Sheets-Sheet 3 INVENTOR.

DAV/0 604 4? tae sawsnze amnonrin raoxnvnry INFRARED no reason nsnrcsron David 3. Edwards, 218 Hawthorne Court, Fort Walton Beach, Fla. Fiied Jan. 3%, 1959, $91. No. 7%,3tl7

3 Claims. (Cl. Ltd-d4} (Granted under Title 35, U5. Code (1952), see. 266) T e invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to an airborne proximity firing error indicator system and more particularly to a system wherein a missile transmitting infrared energy is directed towards an airborne target containing a system providing data relating to the proximity of the aimed missile to the target.

The method and system of providing proximity information is one in which an airborne frangible target is towed by another aircraft. Since the target is being towed, the velocity thereof is known or in the alternative can be precisely controlled and predetermined by the aircraft towing said target. The missile which may be aimed at said target would be conventional and its velocity well known. Therefore the relative velocity of the missile in relation to the target is known or can be easily prearranged. The target has a boom extension attached to its tail. The longitudinal axis of the target its boom extension are identical. The boom extension is generally in the form of an extruded shell. The boom extension is comprised of a material such as lithium fluoride which readily passes infrared energy. The boom extension is blackened to inhibit passage therethrough of infrared energy, except for a cylindrical area providing a desired field of view.

A standard infrared detector, having a cylindrical form, is mounted within the boom extension and is concentric with the unblacliened cylindrical area. The active surface is applied to the detector at its outer cylindrical periphery. The detector is also mounted concentrically within a constant speed, rotating, chopping reticle which is in the form of a slotted drum.

The purpose of the chopping reticle is to provide a reference time base for counting and to provide application of alternating current circuit techniques. The chopping re cle provides a reference base by rotating at a constant speed, and since the infrared detector is located concentrically therein, its output, if infrared energy is present in the aforesaid field of view, will be a series of electrical pulses whose frequency is proportional to the chopping rate. By keeping the rotational speed of the chopping reticle constant, the number of electrical pulses generated is determined by the length of time the missile energy is present in the field of view of the infrared detector located in the frangible target; and since the field of view is fixed, the number of electrical pulses generated is representative of the distance from the aimed missile to the infrared detector. It is to be noted when the missile approaches the target in a plane perpendicular to the longitudinal axis of the target, the missile may not pass through the fiield of view of the detector and thus no pulses will be generated, or the missile may pass through the field of view in a plane perpendicular to the longitudinal axis of the target but cause more pulses to be generated than a missile pass ing through the field of a view in a plane parallel to the longitudinal axis of the target at the same distance from the target.

Because the frangible target rotates at a rate deter- Patented Jan. 29, 1953 mined by its towing speed and the angle of its fins, it is necessary to account for this rotational velocity.

A correction may be applied by determining the revolutions per second of the frangible target. The apparatus to achieve this objective is provided by a mirror attached to a tow cable which is connected between the towing aircraft and towed target. This mirror does not rotate since it is attached to a swivel on the nose of the frangible target to prevent rotation of the cable. A small light source is placed on the nose of the towed target so that its energy can strike the mirror. From the mirror, the energy is reflected to a second infrared etector also located on the nose of the towed target.

The light and the detector rotate at the speed of the frangible target since they are an integral part of the target, while the mirror is stationary. Therefore, for each revolution of the target, the energy from the light source is reflected to the detector by the mirror. Consequently, the number of revolutions of the target is counted by referencing the output of the first infrared energy detector to a time base.

The number of slots in the outer periphery of the aforesaid chopping reticle is governed by the time constant of the infrared detector enclosed therein. The shorter the time constant, the greater the number ofslots that may be used, and consequently, the greater the accuracy. Of course the speed of the constant speed motor must be compatible with the number of slots selected. The slots for the chopping reticle may be either etched or punched, and the accuracy of the system is determined primarily by the accuracy of the slots themselves. .2

An object of the present invention is to provide a novel infrared airborne system for scoring missile firings at airborne towed targets wherein the towed target rotates.

Another object of the present invention is to provide an airborne infrared system located in a towed rotating target for detecting infrared energy transmitted by an aimed missile directed at the towed target and converting the received infrared energy into electrical data representative of the proximity of the aimed missile to the towed target.

A still further object of the present invention is to provide an infrared system located in an airborne, towed, rotating target for determining the proximity of an aimed missile to the towed target.

Yet another object of the present invention is to provide an infrared airborne system for determining the proximity of an aimed missile to an airborne target wherein the system is located in the towed target and including automatic means for correcting the proximity data as errors occur as a result of the rotation of said towed target.

The novel features that I consider characteristic of my invention are set forth with particularity in the ap-' pended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will be understood from the following description of specific embodiments thereof when read in conjunction with the accompanying drawings, in which:

FIGURE 1 shows a view of the towed target having a boom extension attached to and extending from its terminal end and a towing cable attached to its nose;

FIGURE 2. is a diagrammatic view partly in section showing the boom extension including apparatus therein to generate output data relative to the proximity of missile aimed thereat;

FIGURE 3 shows a perspective view of the chopping reticle and its associated infrared detector which are included in the boom extension;

FIGURE 4 shows the nose of the towed target and the towing cable attached thereto and including apparatus producing rotational data relating to the towed target;

FIGURE shows the surface of the circular flange facing the towed target; and

FiGURE 6 shows proximity data recorded on a time baseline as a missile is fired through the fleld of view of the towed target and also shows rotational data for the towed target.

Referring now to the drawings in detail, there is shown in FIGURE 1 the towed target 1. Integral with towed target 1 is boom extension 2 which is attached and extends from the terminal end thereof. Baseline 3 represents the longitudinal axis of towed target 1 and boom extension 2. Nose 4 of towed target 1 is shown with towing cable 5 attached thereto.

Now referring to FIGURE 2, there is shown a diagrammatic view partly in section of the boom extension 2 which is the boom extension shown in FIGURE 1. Boom extension 2' is shown with longitudinal axis 3'. Boom extension 2 is comprised of extruded shell 6 of generally cylindrical contour closed at its outboard end by semi-spherical closure plate 7 having at its center bearing element 3 as an anchorage for horizontally extending post 9 carrying at its inboard end an infrared detector iii of generally cylindrical shape whose outer surface is coated with active surface 11. Surface 11 is comprised of conventional material utilized to detect infrared energy. Extending post 9 is constructed of nylon based Bakelite. Extruded shell 6 and semi-spherical closure plate 7 are comprised of lithium fluoride which will readily permit infrared energy to pass therethrough. Any material having similar properties as lithium fluoride may be substituted therefor. Extruded shell 6 and semi-spherical closure plate 7 are coated black to prevent infrared energy from penetrating therethrough. Area 12 of extruded shell 6 remains uncoated and thereby permits free access of infrared energy into the interior of boom extension 2' within the confines of the aforementioned area. Area 12 is of cylindrical shape. Infrared detector 19 is so positioned by extending post 9 as to be concentric with unblackened, cylindrical, area 12.

Chopping reticle 13 is in the form of a drum with end wall 14 open. Reticle 13 is provided with hollow driven shaft 15 which is integral therewith. Bearing 16 is affixed to extruded shell 6 by suitable bolts and serves to position the cylindrical portion of chopping reticle 13 so that infrared detector 19 is mounted concentrically therein and also so that it is concentric with unblackened area 12.

Motor 17 is concentrically positioned within extruded shell 6 by mounting base 18. Mounting base 18 is attached to shell 6 by any suitable means such as bolts. Driving shaft 1.9 is splined at its outer end and is attached to driven shaft 15 by coupler 20. V

Coupler 20 is comprised of three nylon based Bakelite elements 21, 22 and 23. Element 22 is in the shape of a cylinder having thereupon pressure fitted copper plate 24. Element 23 is in the shape of a cylinder open at one end to receive the splined end of driving shaft 19. Element 21 is in the form of a cylinder open at one end to receive shaft 25. Elements 21, 22 and 23 are clamped together by suitable bolts and nuts such as 26 and 27. Shaft is comprised of an electrical conductor such as aluminum and is attached to infrared detector 16 both physically and electrically so that it is integral therewith. Bearing element 28 consists of nylon based Bakelite and serves to hold shaft 25 concentrically within hollow driven shaft 15. Shaft 25 has attached thereto metal spring and ball retainer 29. Spring 30 is enclosed in retainer 29 and is fitted into spring guide 31. Metal ball 32 is thereby pressed firmly against copper plate 24 to make electrical contact. Metal ball 32 is free to rotate. Brush retainer 33 is affixed to extruded shell 6 by suitable bolts and screws and serves as a container for brushes 34 and 35 which are in contact with copper plate 24-. Brush retainer 33 is comprised of nylon based Bakelite. Metal lugs 36 and 37 are attached electrically to brushes 34 and 35 respectively. Lugs 36 and 37 are connected together electrically by line 38 and then connected to amplifier 39, which provides an output to line 4i Line 49 is connected to output jack 41. Amplifier 3% is bolted to extruded shell 6. y

Now referring to FIGURE 3, chopping reticle i3 is comprised of a drum with outer end 14- open to receive infrared detector 19. Detector it) is positioned concentrically within chopping reticle 13 by means of post 9. Chopping reticle 13 has a number of slots located in its outer periphery. Slot 32 is representative of all the slots located in the outer periphery of reticle 13. The slots may be formed either by punching or etching depending upon the material used.

Now referring to FIGURE 4, there is shown a side view of nose 4' of the towed target. Riveted to nose 4' is rotatable yoke 43. A swivel coupling is provided by enclosing the extremity of coupling pin 44 in rotatable yoke 43. Ball bearings 46 are provided for facilitating rotation. Limit collar 47 is provided for the swivel coupling. Coupling pin 44 is attached to flange 48 by means of rivets. Flange 48 consists of a circular steel casting. Coupling yoke 49 is attached to flange 48 by suitable studs. To coupling yoke 4-9 is connected towing cable 5'. A light reflecting surface, facing towards nose 4, is provided on the surface of flange 48. The light reflecting surface is in the shape of segment of a disc as illustrated in FIGURE 5.

Now referring to FIGURE 5, there is shown circular steel flange 4-8. Segmental disc 56 consists of a material that reflects light. Segmental disc 50 is on the surface of flange 48' that faces the nose of the towed target. The remaining surface of flange 48, exclusive of disc 50, is coated black so as not to reflect light.

Now referring again to FIGURE 4, light source 51 is mounted in semi-spherical closure plate 7' so that its light energy is directed at the light reflecting disc on flange 4%. Infrared detector 52 is mounted in semi-spherical closure plate 7' so that it received light energy reflected from the aforesaid disc. Electrical line 53 is provided from infrared detector 52 to jack 53'. A plug with a connecting electrical linemay be inserted into jack 53' thereby providing means for relaying the signal from infrared detector 52 to an oscilloscope mounted in a towing plane. Light source 51 and infrared detector 52 rotate at the speed of the towed target as they are integral therewith while the aforesaid reflecting disc remains stationary. Therefore, for each revolution of the towed target, the energy from light source 51 is reflected to infrared detector 52 by the light reflecting disc on the surface of flange 43, and consequently the number of revolutions of the towed target is counted by referencing the output signal from infrared detector 52 to a time base as provided by an oscilloscope in the towing plane. Therefore the revolutions per second of the towed target may be thus determined.

Again referring to FIGURE 2, field of view 54 has the shape of a rotating cone whose central axis defines, as it rotates; a plane normal to longitudinal axis 3. The aforesaid field of view is provided by permitting infrared energy to pass through uncoated area 12 of extruded shell 6 and by concentrically mounting rotatable, chopping reticle 13 within area 12.

As an aimed missile transmitting infrared energy passes through field of view 54, chopping reticle 13 is being rotated at a constant rate of speed by motor 17. Electrical pulses are generated when infrared energy from aforesaid aimed missile is transmitted to infrared detector 1ft through the aforementioned slots on the outer periphery of rotating, chopping reticle 13. The number of electrical pulses generated is determined by the length of time the aimed missile is in field of view 54%, and sin e t fi field of view is conical around 360", the time the aforesaid missile is in the field of view and consequently the number of electrical pulses generated is representative of the distance from the missile to detector 10.

The output of infrared detector is comprised of electrical pulses which are transmitted along shaft through spring and ball retainer 29 to metal rotating ball 32. From ball 32, the electrical pulses are fed to rotating copper plate 24 and thence to lugs 36 and 37 by way of brushes 34 and 35 respectively. Electrical line 38 interconnects lugs 36 and 37 and then feeds amplifier 39 with aforesaid electrical pulses originating from infrared detector 10. The amplified pulses are fed to jack 41 by way of line 40. A plug with a connecting electrical line may be inserted into jack 41 and then fed to aforementioned oscilloscope which is mounted in the towing plane.

Referring now to FIGURE 6, there is shown towed target 1" having boom extension 2" integral therewith. Boom extension 2" and its included apparatus is identical to the boom extension and apparatus described for FIGURE 2. Field of view 54" is shown being cut by aimed missile 56 at points 57 and 58. A time base line is provided, as by an oscilloscope in a towing plane, and the number of electrical pulses generated during the period of transmission of infrared energy from missile 56 during the period it is in field of view 54" between points 57 and 53 is recorded on time base line 59. The number of electrical pulses supply the requisite data for determining the proximity of missile 56 from towed target 1".

Because the towed target rotates at a rate determined by towing speed and angle of its fins, it is necessary to account for this rotational velocity and apply it as a correction to the number of electrical pulses recorded on time base line 59.

An electrical pulse is supplied for each revolution of towed target 1" since light source 51" and infrared detector 52" rotate at the speed of towed target 1" while the light reflecting disc on flange 48" remains stationary. Therefore, for each revolution of towed target 1", the energy from light source 51 is reflected to detector 52" by the aforesaid light reflecting disc, and consequently the number of revolutions of towed target 1" is counted by referencing the output of infrared detector 52" to time baseline 60, which may also be supplied by the aforesaid oscilloscope mounted in the towing plane. The revolutions per second of towed tar-get 1" may be determined as shown in FIGURE 6 for a rotational speed of 300 r.p.m.

It is to be noted that the slots in the chopping reticle, previously described, are governed by the time constant of their associated infrared detector. The shorter the time constant, the greater the number of slots that may be utilized; and consequently the greater the accuracy. The speed of the constant speed motor rotating the chopping reticle must be compatible with the number of slots selected. The slots may be either etched or punched, and the accuracy of the system is determined primarily by the accuracy of the slots themselves.

What is claimed is:

1. Means for recording pulses representative of target rotation; in a target rotation measuring system wherein said target is being towed and is also undergoing continuous rotation in space, pulse recording means comprising swiveling means attached to the the nose of said towed target, a towing cable with an associated flange connected to said swiveling means, a segment of a light reflecting disc applied to the surface of said flange, said segment of said disc positioned to face said nose of said target, a light source mounted in said nose so that its light energy is directed towards said segment of said light reflecting disc, infrared detector means also mounted in said nose and being positioned to receive the energy reflected from said segment of said light reflecting disc and thus operating to emit a pulse on each revolution of said target, indicating means for establishing a time base indicator to serve as reference means for measuring the pulse output of said infrared means, and means to record on said indicating means the pulse output from said infrared means.

2. Means for recording pulses representative of target rotation in a target rotation measuring system wherein said target is undergoing continuous rotation in space, said rotation recording means comprising a segment of a stationary light reflecting disc facing the nose of said target, a light source mounted in the nose of said target, said light source having its light energy directed at said segment of said light reflecting disc, infrared detector means also mounted in said nose, said infrared means being positioned to receive the light energy reflected from said segment of said light reflecting disc and thus operating to emit a pulse on each revolution of said target, indicating means for establishing a time base indication to serve as reference means for measuring the pulse output of said infrared means and means to record on said indicating means the pulse output from said infrared means.

3. Means for recording pulses representative of target rotation in a target rotation measuring system wherein said target is being towed and is also undergoing continuous rotation in space, said pulse recording means comprising means to generate electrical pulses representative of the rate of rotation of said target, means to record said pulses representative of said rotation rate on a time base line wherein said means to generate electrical pulses representative of the rate of rotation of said target is comprised of swiveling means attached to the nose of said tow target, a towing cable with an associated flange connected to said swiveling means, a segment of a light reflecting disc applied to the surface of said flange, said segment of said disc positioned to face said nose of said target, a light source mounted in said nose so that its light energy is directed towards said segment of said light reflecting disc, and infrared means also mounted in said disc and being positioned to receive the energy reflected from said light 55 reflecting disc.

References Cited in the file of this patent UNITED STATES PATENTS 2,405,597 Miller Aug. 13, 1946 

1. MEANS FOR RECORDING PULSES REPRESENTATIVE OF TARGET ROTATION; IN A TARGET ROTATION MEASURING SYSTEM WHEREIN SAID TARGET IS BEING TOWED AND IS ALSO UNDERGOING CONTINUOUS ROTATION IN SPACE, PULSE RECORDING MEANS COMPRISING SWIVELING MEANS ATTACHED TO THE NOSE OF SAID TOWED TARGET, A TOWING CABLE WITH AN ASSOCIATED FLANGE CONNECTED TO SAID SWIVELING MEANS, A SEGMENT OF A LIGHT REFLECTING DISC APPLIED TO THE SURFACE OF SAID FLANGE, SAID SEGMENT OF SAID DISC POSITIONED TO FACE SAID NOSE OF SAID TARGET, A LIGHT SOURCE MOUNTED IN SAID NOSE SO THAT ITS LIGHT ENERGY IS DIRECTED TOWARDS SAID SEGMENT OF SAID LIGHT REFLECTING DISC, INFRARED DETECTOR MEANS ALSO MOUNTED IN SAID NOSE AND BEING POSITIONED TO RECEIVE THE ENERGY REFLECTED FROM SAID SEGMENT OF SAID LIGHT REFLECTING DISC AND THUS OPERATING TO EMIT A PULSE ON EACH REVOLUTION OF SAID TARGET, INDICATING MEANS FOR ESTABLISHING A TIME BASE INDICATOR TO SERVE AS REFERENCE MEANS FOR MEASURING THE PULSE OUTPUT OF SAID INFRARED MEANS, AND MEANS TO RECORED ON SAID INDICATING MEANS THE PULSE OUTPUT FROM SAID INFRARED MEANS. 